Conservation Biology and BiodiversityConservation biology [L. conservatio, keep, save] is a new discipline that studies all aspects of biodiversity with

the goal of conserving natural resources for this generation and future generations. Conservation biology is unique inthat it is concerned with both the development of scientific concepts and the application of these concepts to the every-day world. A primary goal is the management of biodiversity for sustainable use by humans. To achieve this goal, con-servation biologists are interested in, and come from, many fields of biology that only now have been brought to-gether into a cohesive whole:

Applied biology

Like a physician, a conservation biologist must be aware of the latest findings, both theoretical and practical, and beable to use this knowledge to diagnose the source of trouble and suggest a suitable treatment. Often, it is necessaryto work with government officials at both the local and federal levels.

Conservation biology is a unique science in another way. It takes a leap of faith and unabashedly supports thefollowing ethical principles: (1) Biodiversity is desirable for the biosphere and therefore for humans; (2) extinctions, due to human actions, are therefore undesirable; (3) the complex interactions in ecosystems support biodiversity and are desirable; and (4) biodiversity brought about by evolutionary change has value in and of itself, regardless of any practical benefit.

Conservation biology has emerged in response to a crisis—never before in the history of the Earth are so manyextinctions expected in such a short period of time. Estimates vary, but at least 10-20% of all species now livinglost likely will become extinct in the next 20 to 50 years unless immediate action is taken. It is urgently important,then, that all citizens understand the concept of biodiversity, the value of biodiversity, the likely causes of present-dayextinctions, and what could be done to prevent extinctions from occurring.

BiodiversityAt its simplest level, biodiversity [Gk. bio, life; L. diversus, various] is the variety of life on Earth. It is common practice to describe biodiversity in terms of the number of species among various groups of organisms. The Figure above only accounts for the species that have so far been described. It has been estimated that there may be between 5 and 15 million species in all; if so, many species are still to be found and described.

You can well appreciate that simply giving the number of species on Earth is not very meaningful, and certainlyecologists describe biodiversity as an attribute of three other levels ,of biological organization: genetic Aiversity, commu- nity diversity, and landscape diversity.

Genetic diversity refers to variations among the mem- bers of a population. Populations with high genetic diver-sity are more likely to have some individuals that can survive a change in the structure of their ecosystem. Forexample, the 1846 potato blight in Ireland, the 1922 wheat failure in the Soviet Union, and the 1984 outbreak of citruscanker in Florida were all made worse by limited genetic variation among these crops. If a species' populations arequite small and isolated, it is more likely to eventually become extinct because of a loss of genetic diversity.

Community (and therefore ecosystem) diversity is de- pendent on the interactions of species at a particular locale.One community's species composition can be completely different from that of other communities. Communitycomposition, therefore, increases the amount of biodiversity in the biosphere. Although past conservation efforts fre-quently concentrated on saving particular species, such as the California condor, the black-footed ferret, or the spottedowl, this is a shortsighted approach. Saving an en,tire com- munity can save many species, and the contrary is alsotrue—disrupting a community threatens the existence of more than one species. Opossum shrimp (Mysis relicta) wereintroduced into Flathead Lake in Montana and its tributaries as food for salmon. The shrimp ate so much zooplankton that there was in the end far less food for the fish and ultimately for the grizzly bears and bald eagles as well (Fig. 50.2).

Landscape diversity involves a group of interacting ecosystems; within one landscape, for example, there maybe plains, mountains, and rivers. Any of these ecosystems can be so fragmented that they are connected by onlypatches (remnants) or strips of land that allow organisms to move from one ecosystem to the other.

Distribution of DiversityBiodiversity is not evenly distributed throughout the bio- sphere; therefore, protecting some areas will save more

species than protecting other areas. Biodiversity is highest at the tropics, and it declines toward each pole on land, in fresh water, and in the ocean. Also, more species are found in the coral reefs of the Indonesian archipelago than in other coral reefs as one moves westward across the Pacific.

Some regions of the world are called biodiversity hotspots because they contain unusually large concentra-tions of species. Hotspots contain about 20% of the Earth's species but cover only about half of y?o of the Earth's landarea. The island of Madagascar, the'Cape region of South Africa, and the Great Barrier Reef of Australia are all biodi-versity hotspots.

One surprise of late has been the discovery that rain forest canopies and the deep-sea benthos have many morespecies than formerly thought. Some conservationists refer to these two areas as biodiversity frontiers.Conservation biology is the study and sustainable management of biodiversity for the benefit of human beings. Biodiversity is often defined as a variety of life at the species level, but biodiversity is also important at the genetic, community (ecosystem), and landscape levels.

Value of BiodiversityConservation biology strives to reverse the trend toward the possible extinction of thousands of plants and

animals. To bring this about, it is necessary to make all people aware that biodiversity is a resource of immense value.

Direct ValueVarious individual species perform services for human beings and contribute greatly to the value we should

place on biodiversity. Only some of the most obvious values are discussed here and illustrated in Figure 50.3.

Medicinal ValueMost of the prescription drugs used in the United States were originally derived from living organisms. The rosy

periwinkle from Madagascar is an excellent example of a tropical plant that has provided us with useful medicines.Potent chemicals from this plant are now used to treat two forms of cancer: leukemia and Hodgkin disease. Because ofthese drugs, the survival rate for childhood leukemia has gone from 10% to 90%, and Hodgkin disease is usually cur-able. Although the value of saving a life cannot be calculated, it is still sometimes easier for us to appreciate theworth of a resource if it is explained in monetary terms. Thus, researchers tell us that, judging from the success ratein the past, an additional 328 types of drugs are yet to be found in tropical rain forests, and the value of this resourceto society is probably $147 billion. •?,

You may already know that the antibiotic penicillin is derived from a fungus and that certain species of bacteriaproduce the antibiotics tetracycline and streptomycin. These drugs have proven to be indispensable in the treat-ment of diseases, including certain sexually transmitted diseases.

Leprosy is among those diseases for which there is as yet no cure. The bacterium that causes leprosy will not grow in the laboratory, but scientists discovered that it grows naturally in the nine-banded armadillo. Having a source for the bacterium may make it possible to find a cure for leprosy. The blood of horseshoe crabs contains a substance called limulus amoebocytelysate, which is used to ensure that medical devices such as pacemakers, surgical implants, and prosthetic devices are free of bacteria. Blood is taken from 250,000 crabs a year, and then they are returned to the sea unharmed.

Agricultural ValueCrops such as wheat, corn, and rice are derived from wild plants that have been modified to be high producers.

The same high-yield, genetically similar strains tend to be grown worldwide. When rice crops in Africa were being devastated by a virus, researchers grew wild rice plants from thousands of seed samples until they found one that con- tained a gene for resistance to the virus. These wild plants were then used in a breeding program to transfer the gene into high-yield rice plants. If this variety of wild rice had become extinct before it could be discovered, rice cultivation in Africa might have collapsed.

Biological pest controls—natural predators and parasites—are often preferable to using chemical pesticides.When a rice pest called the brown plant hopper became resistant to pesticides, farmers began to use natural brownplanthopper enemies instead. The economic savings were calculated at well over $1 billion. Similarly, cotton growersin Canete Valley, Peru, found that pesticides were no longer working against the cotton aphid because of resistance. Re- search identified natural predators that are now being used to an ever greater degree by cotton farmers. Again, savings have been enormous.

Most flowering plants are pollinated by animals, such as bees, wasps, butterflies, beetles, birds, and bats. The honey- bee, Apis mellifera, has been domesticated, and it pollinates almost $10 billion worth of food crops annually in the United States. The danger of this dependency on a single species is exemplified by mites that have now wiped out more than 20% of the commercial honeybee population in the United States. Where can we get resistant bees? From the wild, of course. The value of wild pollinators to the U.S. agricultural economy has been calculated at $4.1 to $6.7 billion a year.

Consumptive Use ValueWe have had much success cultivating crops, keeping domesticated animals, growing trees in plantations, and so

forth. But so far, aquaculture, the growing of fish and shell- fish for human consumption, has contributed only mini-mally to human welfare—instead, most freshwater and marine harvests depend on the catching of wild animals, suchas fishes (e.g., trout, cod, tuna, and flounder), crustaceans (e.g., lobsters, shrimps, and crabs), and mammals (e.g.,whales). Obviously, these aquatic organisms are an invaluable biodiversity resource.

The environment provides all sorts of other products that are sold in the marketplace worldwide, including wild

fruits and vegetables, skins, fibers, beeswax, and seaweed. Also, some people obtain their meat directly from the environ- ment. In one study, researchers calculated that the economic value of wild pig in the diet of native hunters in Sarawak, East Malaysia, was approximately $40 million per year.

Similarly, many trees are still felled in the natural envi- ronment for their wood. Researchers have calculated that a species-rich forest in the Peruvian Amazon is worth far more if the forest is used for fruit and rubber production than for timber production. Fruit and the latex needed to produce rubber can be brought to market for an unlimited number of years, whereas once the trees are gone, no more timber can be harvested.

Wild species directly provide us with all sorts of goods and services whose monetary value can sometimes becalculated

Indirect ValueThe wild species we have been discussing live in ecosystems. If we want to preserve them, it is more economical

to save the ecosystems than the individual species. Ecosystems perform many services for modern humans, who increas- ingly live in cities. These services are said to be indirect be- cause they are pervasive and not easily discernible (Fig. 50.4). Even so, our very survival depends on the functions that ecosystems perform for us.

Biogeochemical CyclesYou'll recall from Chapter 48 that ecosystems are character- ized by energy flow and chemical cycling. The

biodiversity within ecosystems contributes to the workings of the water, carbon, nitrogen, phosphorus, and other biogeochemical cy- cles. We are dependent on these cycles for fresh water, re- moval of carbon dioxide from the atmosphere, uptake of ex- cess soil nitrogen, and provision of phosphate. When human activities upset the usual workings of biogeochemical cy- cles, the dire environmental consequences include the re- lease of excess pollutants that are harmful to us. Technology is unable to artificially contribute to or create any of the bio- geochemical cycles.

Waste DisposalDecomposers break down dead organic matter and other types of wastes to inorganic nutrients that are used by

the producers within ecosystems. This function aids humans immensely because we dump millions of tons of waste ma- terial into natural ecosystems each year. If it were not for decomposition, waste would soon cover the entire surface of our planet. We can build sewage treatment plants, but they are < expensive, and few of them break down solid wastes completely to inorganic nutrients. It is less expen- sive and more.efficient to water plants and trees with par- tially treated wastewater and let soil bacteria cleanse it completely. ' •

Biological communities are also capable of breaking down and immobilizing pollutants, such as heavy metalsand pesticides, that humans release into the environment. A review of wetland functions in Canada assigned a value of$50,000 per hectare (100 acres or 10,000 square meters) per year to the ability of natural areas to purify water and takeup pollutants.

Provision of Fresh WaterFew terrestrial organisms are adapted to living in a salty environment—they need fresh water. The water cycle

con- tinually supplies fresh water to terrestrial ecosystems. Hu- mans use fresh water in innumerable ways, including drink- ing it and irrigating their crops. Freshwater ecosystems such as rivers and lakes also provide us with fish and other types of organisms for food.Unlike other commodities, there is no substitute for fresh water. We can remove salt from seawater to obtain fresh

water, but the cost of desalination is about four to eight times the average cost of fresh wafer acquired'via fAewater cycle.

Forests and other natural ecosystems exert a "sponge effect." They soak up water and then release it at a regularrate. When rain falls in a natural area, plant foliage and dead leaves lessen its impact, and the soil slowly absorbs it, espe- cially if the soil has been aerated by organisms. The water- holding capacity of forests reduces the possibility offlooding. The value of a marshland outside Boston, Massa- chusetts, has been estimated at $72,000 per hectare per year solely on its ability to reduce floods. Forests release water slowly for days or weeks after the rains have ceased. Rivers flowing through forests in West Africa release twice as much water halfway through the dry season, and between three and five times as much at the end of the dry season, as do rivers from coffee plantations.

Prevention of Soil ErosionIntact ecosystems naturally retain soil and prevent soil ero- sion. The importance of this ecosystem attribute is

especially observed following deforestation. In Pakistan, the world's largest dam, the Tarbela Dam, is losing its storage

capacity of 12 billion cubic meters many years sooner than expected because silt is building up behind the dam due to deforesta- tion. At one time, the Philippines were exporting $100 mil- lion worth of oysters, mussels, clams, and cockles each year. Now silt carried down rivers following deforestation is smothering the mangrove ecosystem that serves as a nurs- ery for the sea. Most coastal ecosystems are not as bountiful as they once were because of deforestation and a myriad of other assaults.

Regulation of ClimateAt the local level, trees provide shade and reduce the need for fans and air conditioners during the summer.Globally, forests ameliorate the climate because they take up carbon dioxide. The leaves of trees use carbon

diox- ide when they photosynthesize, and th|" bodies of the trees store carbon. When trees are cut and burned, carbon dioxide is released into the atmosphere. Carbon dioxide makes a sig- nificant contribution to global warming, which is expected to be stressful for many plants and animals. Only a small percentage of wildlife will be able to move northward, where the weather will be suitable for them.

EcotourismAlmost everyone prefers to vacation in the natural beauty of an ecosystem. In the United States, nearly 100

million people enjoy vacationing in a natural setting. To do so, they spend $4 billion each year on fees, travel, lodging, and food. Many tourists want to go sport fishing, whale watching, boat riding, hiking, birdwatching, and the like. Some want to merely immerse themselves in the beauty of a natural environment.

Biodiversity and Natural EcosystemsMassive changes in biodiversity, such as deforestation, have a significant impact on ecosystem services such as

those we have been discussing. Researchers are interested in deter- mining whether a high degree of biodiversity also helps ecosystems function more efficiently. To test the benefits of biodiversity in a Minnesota grassland habitat, researchers sowed plots with seven levels of plant diversity. Their study found that ecosystem performance improves with increas- ing species richness. The more diverse the plots, the lower the concentrations of inorganic soil nitrogen, indicating a higher level of nitrate uptake. A similar study in California also showed greater overall resource use in more diverse plots.

Another group of experimenters tested the effects of an increase in diversity at four levels: producers, herbivores, parasites, and decomposers. They found that the rate of photosynthesis increased as diversity increased (Fig. 50.4c).

A computer simulation has shown that the response of a de- ciduous forest to elevated carbon dioxide is a function of species diversity. The more complex community, composed of nine tree species, exhibited a 30% greater amount of pho- tosynthesis than a community composed of a single species.

More studies are needed to test whether biodiversity maximizes resource acquisition and retention within anecosystem. Also, are more diverse ecosystems better able to withstand environmental changes and invasions by otherspecies, including pathogens? Then, too, how does fragmen- tation affect the distribution of organisms within an ecosys- tem and the functioning of an ecosystem?

Ecosystems perform services that most likely depend on a high degree of biodiversity.

Causes of ExtinctionIn order to stem the tide of extinction, it is first necessary to identify its causes. Researchers examined the

records of 1,880 threatened and endangered wild species in the United States and found that habitat loss was involved in 85% of the cases (Fig. 50.5fl). Alien species had a hand in nearly 50%, pollution was a factor in 24%, overexploitation in 17%, and disease in 3%. The percentages add up to more than 100% because most of these species are imperiled for more than one reason. Macaws are a good example that a combination of factors can lead to a species decline (Fig. 50.5b). Not only has their habitat been reduced by encroaching timber and mining companies, but macaws are also hunted for food and collected for the pet trade.

Habitat LossHabitat loss has occurred in all ecosystems, but concern has now centered on tropical rain forests and coral reefs

because they are particularly rich in species. A sequence of events in Brazil offers a fairly typical example of the manner in which rain forest is converted to land uninhabitable for wildlife. The construction of a major highway into

the forest first pro- vided a way to reach the interior of the forest (Fig. 50.5c). Small towns and industries sprang up along the highway, and roads branching off the main highway gave rise to even more roads. The result was fragmentation of the once

immense forest. The government offered subsidies to any- one willing to take up residence in the forest, and the people who came cut and burned trees in patches (Fig. 50.5d). Trop- ical soils contain limited nutrients, but when the trees are burned, nutrients are released that support a lush growth for the grazing of cattle for about three years. However, once the land was degraded (Fig. 50.5e), the farmer and his family moved on to another portion of the forest.

Loss of habitat also affects freshwater and marine biodiversity. Coastal degradation is mainly due to the largeconcentration of people living there. Already, 60% of coral reefs have been destroyed or are on the verge of destruction;

it's possible that all coral reefs may disappear during the next 40 years. Mangrove forest destruction is also a problem;

Indonesia, with the most mangrove acreage, has lost 45% of its mangroves, and the percentage is even higher for-other tropical countries. Wetland areas, estuaries, and seagrass beds are also being rapidly destroyed.

Alien SpeciesAlien species, sometimes called exotics, are normative mem- bers of an ecosystem. Ecosystems around the

globe are char- acterized by unique assemblages of organisms that have evolved together in one location. Migrating to a new location is not usually possible because of barriers such as oceans, deserts, mountains, and rivers. Humans, however, have in- troduced alien species into new ecosystems chiefly due to:

Colonization Europeans, in particular, brought various familiar species with them when they colonized newplaces. For example, the pilgrims brought the dandelion to the United States as a familiar salad green.

Horticulture and agriculture Some exotics now taking over ' vast tracts of land have escaped from cultivated areas.

Kudzu is a vine from Japan that the U. S. Department of , Agriculture thought would help prevent soil rosion.The plant now covers much landscape in the South, . including even walnut, magnolia, and sweet gum trees.

Accidental transport Global trade and travel accidentally bring many new species from one country to another.Researchers found that the ballast water released from ships into Coos Bay, Oregon, contained 367 marinespecies from Japan. The zebra mussel from the Caspian Sea was accidentally introduced into the Great Lakes in 1988. It now forms dense beds that squeeze out native mussels.

Alien species can disrupt food webs. As mentioned earlier, opossum shrimp introduced into a lake in Montanaadded a trophic level that in the end meant less food for bald eagles and grizzly bears (see Fig. 50.2).

Exotics on IslandsIslands are particularly susceptible to environmental dis- cord caused by the introduction of alien species.

Islands have unique assemblages of native species that are closely adapted to one another and cannot compete well against ex- otics. Myrtle trees, Myrica faya, introduced into the Hawai- ian Islands from the Canary Islands, are symbiotic with atype of bacterium that is capable of nitrogen fixation. This feature allows the species to establish itself on nutrient-poor volcanic soil, a distinct advantage in Hawaii. Once estab- lished, myrtle trees call a halt to the normal succession of na- tive plants on volcanic soil.

The brown tree snake has been introduced onto a num- ber of islands in the Pacific Ocean (see Fig. 50Aa). The snake eats eggs, nestlings, and adult birds. On Guam, it has re- duced ten native bird species to the point of extinction. On the Galapagos Islands, black rats have reduced populations of giant tortoise, while goats and feral pigs have changed the vegetation from highland forest to pampaslike grasslands and destroyed stands of cactus. Mongooses introduced into the Hawaiian Islands to control rats also prey on native birds (Fig. 50.6). The Ecology Focus on page 933 offers more examples of disruption by alien species.

PollutionIn the present context, pollution can be defined as any envi- ronmental change that adversely affects the lives

and health of living things. Pollution has been identified as the third main cause of extinction. Pollution can also weaken organ- isms and lead to disease, the fifth main cause of extinction. Biodiversity is particularly threatened by the following types of environmental pollution:

Acid deposition Both sulfur dioxide from power plants and nitrogen oxides in automobile exhaust are converted

to acids when they combine with water vapor in the atmosphere. These acids return to Earth as either wetdeposition (acid rain or snow) or dry deposition (sulfate and nitrate salts). Sulfur dioxide and nitrogenoxides are emitted in one locale, but deposition occurs across state and national boundaries. Acid depositioncauses trees to weaken and increases their susceptibility to disease and insects. It also kills small invertebratesand decomposers so that the entire ecosystem is threatened. Many lakes in the northern United States are now lifeless because of the effects of acid deposition.

Eutrophication Lakes are also undey stress due to over- enrichment. When lakes receive excess nutrients dueto runoff from agricultural fields and wastewater from sewage treatment, algae begin to grow inabundance. An algal bloom is apparent as a green scum or excessive mats of filamentous algae. Upondeath, the decomposers break down the algae, but in so doing, they use up oxygen, A decreased amount ofoxygen is available to fish, leading sometimes to a massive fish kill.Ozone depletion The ozone shield is a layer of ozone (Oa) in the stratosphere, some 50 km above the Earth. The

ozone shield absorbs most of the wavelengths of harmful ultraviolet (UV) radiation so that they do not strike the Earth. The cause of ozone depletion can be traced to chlorine atoms (Cl - ) that come from the breakdown of chlorofluorocarbons (CFCs). The best- known CFC is Freon, a heat transfer agent still found in refrigerators and air conditioners today. Severe